Data rep

• There are two types of Caesar cipher: shift ciphers and substitution ciphers.
• Substitution ciphers are a type of Caesar cipher in which letters are randomly replaced.
• In order to decrypt ciphertext, you must know the encryption method used and the key used to encrypt the information.
• The Vernam cipher is an example of a one-time pad cipher, meaning that each key should only ever be used once and is random and at least as long as the plaintext that is to be encrypted.
• Shift ciphers encrypt using a shift of all the letters in the alphabet by the same amount, forming the key.
• The Vernam cipher works by aligning the characters of the plaintext and the key, converting each character to binary, applying a logical XOR operation to the two bit patterns, and converting the result back to a character.
• In the Vernam cipher, the key used to encrypt the plaintext is used again when decrypting.
• One character is always replaced by the same character in a Caesar cipher.
• Caesar ciphers encrypt information by replacing characters.
• The number of samples per second is called the sampling rate and is expressed in Hertz.
• The Nyquist theorem states that the sampling rate of a digital audio file must be at least twice the frequency of the sound.
• Using MIDI allows easy manipulation of music without loss of quality.
• Rather than storing samples of sound, MIDI stores sound as a series of event messages, each of which represents an event in a piece of music.
• Vector graphics represent images using geometric objects and shapes such as rectangles, circles, and lines.
• Enlarging a bitmap image results in a blurry or even pixelated image, whereas enlarging a vector graphic results in no loss of clarity.
• Computers represent sound as a sequence of samples, each of which takes a discrete digital value.
• There are numerous advantages to using MIDI over a sampled recording of a piece of music.
• Musical instrument digital interface, or MIDI, is used with electronic musical instruments which can be connected to computers.
• Vector graphics frequently use less storage space than bitmapped graphics, as information is stored for each shape, rather than for every single pixel in an image.
• Bitmapped graphics are used for storing photographs.
• Vector graphics can be scaled without losing quality.
• The properties (such as fill colour, fill style, and dimensions) of each geometric object or shape in the image are stored in a list.
• Bitmap image files may contain metadata such as the image's width, height, date created, and colour depth.
• Vector graphics are well suited to simple images which use shapes, like company logos, but they’re no use for photographs.
• Event messages could contain information such as the duration of a note, the instrument with which a note is played, how loud a note is (its volume), and if a note should be sustained.
• Natural numbers ℕ = {0, 1, 2, 3…} are a set of numbers containing all positive whole numbers and zero, which can be used to count how many of a certain item you have.
• The symbol for the natural numbers is ℕ.
• The instruments on which notes sound can be changed, notes can be transposed and the duration of notes can be altered.
• MIDI files are often smaller in size than sampled audio files and are lossless, meaning there’s no information lost when music is stored using MIDI.
• Lossy compression involves some information being lost in the process of reducing the file’s size.
• Dictionary-based methods involve appending a dictionary containing repeated data to the file.
• Both run length encoding and dictionary-based methods are most effective on files that contain a lot of repeated data.
• Smaller files can be transferred faster between storage devices or over the internet.
• Data compression is the process of reducing the size of files by removing redundant information.
• In contrast to lossy compression, there is no loss of information when using lossless compression.
• Unencrypted information is referred to as plaintext and encrypted information is called ciphertext.
• Run length encoding (RLE) reduces the size of a file by removing repeated information and replacing it with one occurrence of the repeated information followed by the number of times it is to be repeated.
• The disadvantages of using MIDI include its inability to store speech and sometimes results in a less realistic sound than sampled recordings.
• The size of a file can be reduced without decreasing its quality using lossless compression methods such as run length encoding and dictionary-based methods.
• Images are often compressed, but sound files and text files can also be compressed.